calls romney's $5 trillion tax plan. darren gersh, tonight, looks at what the real impact of the romney tax plan could be on the american economy. >> reporter: here's where the president gets that $5 trillion number he used again today. governor romney's plan to cut tax rates by 20% would add up to about $5 trillion over ten years, assuming no other changes. but governor romney is planning to make other changes by eliminating tax deductions worth about the same amount. but the president is accurate when he says governor romney is making many promises in his tax plan. romney says upper-income people will not get a net tax cut; middle-income people will not see their taxes go up; incentives for savings and investment won't be touched; the estate tax and alternative minimum tax will be eliminated-- all this while cutting tax rates and not changing the amount of money the federal government brings in. an analysis by the tax policy center shows governor romney will have to make some big tradeoffs. >> so, governor romney has m